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It coincided with a dramatic change in the rodents' behaviour. Given the choice of two environments, mice switched preferences to the one where they had received the cocaine shot.

‘This gives us a possible mechanism for how drug use fuels further drug-seeking behaviour,’ said Dr Linda Wilbrecht, who led the research at the University of California at San Francisco.

Dependent decisions: The effect on the brain means addicts will be biased towards situations and environments associated with cocaine

‘It's been observed that long-term drug users show decreased function in the frontal cortex in connection with mundane cues or tasks, and increased function in response to drug-related activity or information.

‘This research suggests how the brains of drug users might shift towards those drug-related associations.’

The neurons directly affected by cocaine use had the ‘potential to bias decision-making’, she added.

Initially the mice were given access to two adjoining ‘conditioning’ chambers, one smelling of cinnamon and the other vanilla, decorated with different patterns and textures.

Free to explore both compartments, individual mice settled on one they preferred.

They were then injected with cocaine while in the opposite compartment, and given the same choice.

After being given cocaine, each mouse chose the compartment associated with the drug injection.

The study, by U.S. scientists, saw dramatic changes in the preferences of mice once they associated an environment with cocaine

‘When given the choice, most of the mice preferred to explore the side where they had the cocaine, which indicated that they were looking for more cocaine,’ said Dr Wilbrecht.

‘Their change in preference for the cocaine side correlated with gains in new persistent spines that appeared on the day they experienced cocaine.

‘The animals that showed the highest quantity of robust dendritic spines showed the greatest change in preference towards the chamber where they received the cocaine.

‘This suggests that the new spines might be material for the association that these mice have learned to make between the chamber and the drug.’

The findings are published in the latest edition of the journal Nature Neuroscience.